public class Test {

    public class TreeNode {
      int val;
      TreeNode left;
      TreeNode right;
      TreeNode(int x) { val = x; }
    }
    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
        if(root == null) return null;
        if(root == p || root == q) return root;

        TreeNode leftTree = lowestCommonAncestor(root.left,p,q);
        TreeNode rightTree = lowestCommonAncestor(root.right,p,q);

        if(leftTree!=null&&rightTree!=null) {
            return root;
        }else if(leftTree!=null) {
            return leftTree;
        }else {
            return rightTree;
        }
    }

}
